V2X promises to increase the level of vehicle safety by enabling reliable and early alerts of dangerous situations. The V2X band (5.9 GHz) includes three channels in Europe totaling 30 MHz, and seven channels in the US totaling 70 MH. The expansion of the usage of V2X services through the activation of more V2X channels is needed to support additional connectivity services, like vehicle to infrastructure (V21) or automated driving. This needs to be done while assuring that the V2X safety channel communication range is not degraded. As used hereinbelow, “communication range” refers to distance between two communication devices or units.
DSRC (Dedicated Short Range Communication), specified by the IEEE802.11p standard and its upper layer coordination standard IEEE1609.4, ignores the mutual interferences between different channels (i.e. channels using the same 70 MHz band in the US or the same 30 MHz band in Europe). C-V2X is a competing V2X specification, defined by 3GPP. In C-V2X, transmissions are in pre-scheduled timeslots, without checking if any other transmission is currently taking place in same channel or other channels. If allowed for usage, it will share the same band. C-V2X supports multi-user allocation.
The impact of mutual interferences between two channels on the communication range can be explained using simulations. FIG. 1A illustrates a layout of three simulated vehicles, a first vehicle 102, a second vehicle 104 and a third vehicle 106. Vehicle 102 has two receivers R1 and R1 receiving respectively in channels Ch.A and Ch.B. Vehicle 104 has a transmitter T1 transmitting in Ch.A, and vehicle 106 has a transmitter T2 transmitting in Ch.B. Transmitters T1 and T2 transmit concurrently. FIGS. 1B and 1C show simulations of the impact of mutual interferences between two channels Ch.A and Ch.B on the communication ranges. The simulations were performed with the following parameters/conditions: urban environment; WINNER II path-loss model for line of sight (LOS); MCS2 (QPSK R=1/2); target Signal to Noise Ratio (SNR)=6 dB; adjacent channel rejection (ACR)=25 dB and co-adjacent rejection=39 dB (enhanced sensitivity); receiver noise figure: 9 dB; mask C; transmission power=20 dBm.
The horizontal (e.g. X) axis in each of FIGS. 1B and 1C represents the distance d1 112 of transmitter T1 in vehicle 104 from receiver R1 in vehicle 102. The vertical (e.g. Y) axis in each represents the distance d2 114 of transmitter T2 in vehicle 106 from receiver R2 in vehicle 102. Monochromatic grey represents a no-reception zone. The darker grey with changing tone represents zone of reception. It can be seen that the reception of the first channel fails when the second channel transmitter is close to the receiver, while the first channel transmitter is further away. For example, in FIG. 1A, when d2 is less than 30 m, Ch.A reception will fail for distances d1 greater than 150 m. As a result, the communication range is decreased. Here and below, the terms “first” and “second” with respect to channels are used in the context of channels inside a vehicle.
The interference problem is illustrated using a network simulation with a layout shown in FIG. 2A. Vehicles 201-280 are placed 25 meters apart on a two-lane road. Each vehicle has two transmitters and two receivers, assigned to different channels. The two transmitters work independently. Simulation results are shown in FIGS. 2B and 2C. FIG. 2B shows the communication range when two channels in the network are adjacent, and FIG. 2C shows the communication range when the two channels are co-adjacent. To clarify, adjacent channels are allocated sequentially. No guard separates between the end of one and the start of the other. Co-adjacent channels are separated by at least one channel. FIGS. 2B and 2C show histograms where the X-axis represents the communication range in meters and the Y-axis represents occurrences of the recorded communication range at each distance. The simulated vehicle network model applies a two-ray channel model, transmission power of +23 dBm, receive sensitivity of −95 dBm, and channel load of 20% in Ch.A and 40% in Ch.B. The overall (total) number of transmissions in the simulation is 4000. The adjacent channel rejection follows the enhanced values of IEEE802.1p, which are 25 dB for adjacent and 39 dB for co-adjacent. In both the adjacent and co-adjacent cases, the communication range of a vehicle is decreased due to interference from concurrent adjacent channel transmission of another vehicle. The communication range without adjacent channel rejection is above 400 m. Interferences decrease the communication range. The histogram occurrences in each communication range are added up to a given distance, for example up to 200 m, 300 m and 400 m. For example, in FIG. 2A, the communication range drops below 300 m in 1086 transmissions, which is −27% of the total transmissions. The communication range drops below 200 m in 856 transmissions, which are ˜21% of the total transmissions.
The mutual interference may be between a DSRC channel and another DSRC channel or between a DSRC channel and a C-V2X channel.
A high percentage of dropped messages at short distances (e.g. 200 m and 300 m) from the transmitting vehicle are unsatisfactory for safety operation. There is therefore a need for, and it would be advantageous to have apparatus and methods to mitigate (reduce) interferences in transmission and/or reception (also referred to as “usage”) between DSRC channels or between DSRC and C-V2X channels beyond the known art.